In a heat transfer system using a thermal printing head, a substrate comprising a paper or a heat-resistant plastic film, such as a polyester film, having a thickness of about 10 .mu.m and coated with a hot melt colored ink containing a coloring agent, such as a pigment, is heated with a thermal printing head from the side of the substrate to soften and melt the ink, whereby the hot melt ink is transferred to the surface of a receiving material such as a receptive paper.
The conventional hot melt colored ink used in a heat transfer layer of a heat transfer recording material generally contains an ink binder comprising a wax having a melting point of 50.degree. C. to 90.degree. C., a dispersant and a thermoplastic resin such as an ethylene-vinyl acetate copolymer (EVA resin) and a coloring component such as a pigment and a dye. In the conventional hot melt colored ink, EVA resin is an essential component as the ink binder. Consequently, irritating odor generated during the process of mixing and kneading components under heating to produce the hot melt colored ink causes deterioration in work place. Further, EVA resin tends to increase cost for producing a hot melt colored ink.
As a binder for a hot melt colored ink, waxes have been employed. Such waxes include natural waxes such as carnauba wax, candelilla wax, bees wax and montan wax, mineral oil type waxes such as paraffin wax and microcrystalline wax, and synthetic waxes such as polyethylene wax and oxidation wax. Since all of these waxes have poor compatibility with other components, low molecular weight and low melt viscosity, the conventional ink binder has insufficient solubility and dispersibility for a coloring pigment. Furthermore, a hot melt colored ink containing a wax as an ink binder has disadvantages such as grimes, poor sharpness, blurs and stains because of low hardness (needle penetration) and low melt viscosity of the ink. The hot melt colored ink containing a wax has also disadvantages such that the peel strength, unevenness and performance (quality and resolution of the transfer recorded image) of the image printed on a recording material (a receptive paper) are insufficient.